i    ,CI-  ^  :  -*^  s&r^  R-    L-    LANGENHEIM,  J 

\p      }Li  DEPT-  GEOL.  UNIV.  ILLINOIS 

^   .  254  N.  H.  B.,  J 301  W.  GREEN  ST 

URBANA,  ILLINOIS  61801 

Proas  Bulletin  Series  T  .  ,.,     . 

Issued    1  wice  Quarterly 

STATE  OF  ILLINOIS 

DEPARTMENT  OF  REGISTRATION  AND  EDUCATION 

A.  M.  SHELTON,  Director 

DIVISION  OF  THE 

STATE  GEOLOGICAL  SURVEY 

M.  M.  LEIGHTON,  Chief,  Urbana 


No.  14 


ILLINOIS  PETROLEUM  March  n 


1928 


STRUCTURE  AND  OIL  PROSPECTS  OF  EASTERN 
CLARK  COUNTY 
By  Gail  F.  Moulton  and  Jackson  Young 

Introduction 

Following-  the  early  development  of  the  main  eastern  Illinois  oil  fields 
in  1906,  1907,  1908,  and  1909,  there  was  some  haphazard  drilling  in  eastern 
Clark  County.  J  he  various  wells  drilled  at  this  time  were  mainly  shallow 
only  testing  the  possible  oil-bearing  formations  to  a  depth  of  1000  feet 
Although  a  deep  well  in  Terre  Haute,  Indiana,  had  been  producing  oil  from 
the  upper  part  of  the  Devonian  limestone  for  more  than  20  years  at  that  time 
other  wells  drilled  nearby  had  resulted  in  failures,  and  the"  operators  in  Illi- 
nois were  not  willing  to  spend  the  additional  money  required  for  deeper  tests 


Fig  1.     Index  map 


There  was  considerable  drilling  i„  Clark  County  in  1925  and  1926  when 
^operators  were  busy  developing  the  proved  deep  producing  area  south- 
ron V  n  7e  Pr°dUCti0n  had  jUSt  been  discovered  -  the  «PPer 
one  of  the  Devonian  limestone  (call  "Niagaran"  and  "Corniferous"  by 
various  drillers).  By  the  end  of  the  latter  year  very  few  undrilled  locations 
remained,  and  interest  in  the  area  had  practically  disappeared.  Late  in  126 
however,  ,  well  dn  led  in  sec.  6,  T.  9  N..  R.  l0  W.,  Sullivan  County,  India  a' 
-btamed  a  production  of  about  50  barrels  per  day  of  very  light  'oil  accom 


2  ILLINOIS    PETROLEUM 

panied  by  sufficient  gas  to  cause  the  well  to  flow.  The  producing  zone  is  in 
the  upper  part  of  the  Devonian  lime  and  was  found  at  a  depth  of  a  little 
more  than  2100  feet.  The  owners  of  the  discovery  well  formed  the  Siosi 
Oil  Corporation,  and  proceeded  with  the  development  of  the  remainder  of 
the  favorable  acreage,  which  apparently  was  all  under  their  control.  Up  to 
the  present  time  about  15  wells  have  been  completed  which  had  reported 
initial  productions  ranging  from  35  to  100  barrels. 

As  a  result  of  the  discovery  in  Indiana,  considerable  interest  was 
aroused  in  eastern  Clark  County,  and  at  least  two  new  wells  were  drilled  in 
the  hope  of  finding  extensions  of  the  Indiana  pool. 

Geological  conditions  affecting  oil  accumulation  in  eastern  Clark  County 
have  not  been  well  understood,  except  in  a  very  general  way,  because  of  lack 
of  satisfactory  data.  The  recent  drilling  has  provided  new  data  which  per- 
mit a  more  accurate  determination  of  structure  and  stratigraphy.  It  is  the 
purpose  of  this  report  to  make  this  new  information  available  for  the  use 
of  the  oil  operators.  To  that  end  a  structure  map  has  been  prepared  to  show 
the  configuration  of  the  top  of  the  Devonian  limestone,  a  program  of  struc- 
ture drilling  is  herein  recommended,  and  an  area  favorable  for  testing  is 
described.  The  relation  of  the  area  described  in  this  report  to  the  main 
southeastern  Illinois  oil  fields  is  shown  in  figure  1. 

Geology 
stratigraphy 

The  general  stratigraphic  sequence  typical  of  the  region  is  well  illus- 
trated by  the  cross-section  accompanying  this  report  (fig.  2).  Additional 
details  of  the  characteristic  conditions  in  the  eastern  part  of  Clark  County 
are  given  in  the  log  of  the  Wernz  well,  sec.  22,  T.  1 1  N.,  R.  11  W.,  which  is 
published  as  part  of  this  report  because  it  is  the  deep  well  nearest  the  favor- 
able area. 

Driller's  log  from  well  on  Wernz  farm  in  sec.  22,  T.  11  N.,  R.  11  W. 

Barometric  elevation — 606  Feet 

Thickness     Depth 

No.  Feet  Feet 

Pleistocene  system 

1.  Soil,  sandy   8  8 

2.  Gravel,  brown,  hard,  fresh  water 

Pennsylvanian  system 

3.  Shale,   green,   soft 

4.  Sand,  gray,  hard,  fresh  water 

5.  Mud,   blue,   soft 

6.  Mud,  green,  soft 

7.  Red  rock,  red,  soft 


28 

36 

39 

75 

8 

83 

77 

160 

30 

190 

7 

197 

STRUCTURE    AND   (HI.    PROSPECTS    OF    EASTERN    CLARE    COUNTY 
Driller's  loy  from   well  on   Wcrnz  farm   in  sec.  22,  T.  11  N.,  R,  11  W. — Continued 


Barometric  elevation — 606   Feet 

No. 

8.  Mud,  blue,   soft 

9.  Sand,  gray,  hard,  dry 

10.  Lime,  gray,   hard 

11.  Slate,   blue,    soft 

12.  Shale,  sandy,  gray,  hard 

13.  Coal,   black,  soft 

14.  Slate,  gray,  soft 

15.  Lime,   gray,   hard 

16.  Slate,  gray,  soft 

17.  Coal,  black,  soft 

18.  Lime,   gray,   hard 

19.  Shale,  gray,  soft 

20.  Lime,   gray,   hard 

21.  Coal,  black,  soft 

22.  Slate,   blue,   soft 

23.  Shale,  gray,  soft 

24.  Shale,  black,  soft 

25.  Slate,  gray,  soft 

26.  Sand,  gray,  hard,  dry 

27.  Slate,  gray,  soft 

28.  Coal,  black,  soft 

29.  Slate,  blue,   soft 

30.  Slate,   gray,   soft 

31.  Lime,   gray,   hard 

32.  Sand,  broken,  gray,  hard,  dry 

33.  Slate,   blue,    soft 

34.  Slate,  gray,  soft 

35.  Lime,  gray,  hard 

36.  Slate,   gray,   soft 

37.  Sand,  gray,  hard ;  salt  water 

38.  Slate,   blue,   soft 

39.  Slate,   gray,   soft 

40.  Slate,  blue,  soft 

41.  Sand,   gray,    hard 

42.  Slate,  blue,   soft 

43.  Lime,  sandy,  gray,  hard 

Mississippian  (?)  system 

Chester  (?)  series 

44.  Slate,    blue,    soft 

45.  Lime,  shell,  gray,  hard 

46.  Slate,    blue,    soft 

47.  Lime,  brown,  hard 

48.  Slate,  gray,  soft 

Lower  Mississippian  system 

Lime  series 

49.  Sand,  gray,  hard;  salt  water  (probably  lime) 

50.  Slate,   blue,   soft 


Thickness 

Depth 

Feet 

Feet 

13 

210 

40 

250 

3 

253 

52 

305 

97 

402 

5 

407 

8 

415 

6 

421 

14 

435 

5 

440 

5 

445 

35 

480 

2 

482 

2 

484 

4 

488 

42 

530 

10 

540 

35 

575 

10 

585 

22 

607 

5 

612 

25 

637 

10 

647 

6 

653 

7 

660 

10 

670 

130 

800 

5 

805 

15 

820 

15 

835 

10 

845 

15 

860 

30 

890 

17 

907 

3 

910 

12 

922 

28 

950 

5 

955 

15 

970 

10 

980 

20 

1000 

50 

1050 

7 

1057 

ILLINOIS    PETROLEUM 


Driller's  log  from  well  on  Wernz  farm  in  sec.  22,  T.  11  N.,  R.  11  W. — Concluded 


Barometric  elevation — 606  Feet 

No. 

51.  Sand,  gray,  hard;  salt  water  (probably  lime) 

52.  Slate,   blue,   soft 

53.  Lime,  brown,  hard 

54.  Sand,    gray,   hard 

55.  Slate,  green,  soft 

56.  Lime,  white,  hard 

57.  Lime,  gray,  very  hard 

58.  Lime,  brown,   hard 

59.  Lime,  gray,  and  white 

60.  Lime,  brown 

61.  Lime,  gray,  broken,  hard 

62.  Lime,  gray,  very  hard 

63.  Lime,  sandy,  gray,  very  hard;  salt  water 

64.  Lime,  gray,  hard 

65.  Lime,  white,  hard 

66.  Lime,  sandy,  very  hard;  salt  water 

67.  Lime,  black,  hard 

68.  Lime,  slate  break,  black,  hard 

Mississippian-Kinderhook  shales 

69.  Slate,  blue,  soft 

70.  Shale,   black,  hard 

71.  Sand,  gray,  hard;   salt  water  1923 

72.  Shale,  black,   break 

73.  Sand,  gray,  hard;  little  salt  water 

74.  Slate,   black,   hard 

75.  Slate,    blue,    soft 

76.  Sand,  gray,  hard;   little  salt  water 

77.  Shale,  black,  hard 

78.  Lime,   gray,   hard 

79.  Slate,   black,    soft 

80.  Slate,   blue,   soft 

Devonian-Sweetland  Creek  shale 

81.  Lime,  gray,  hard 

82.  Shale,   brown,   soft 

Devonian-Onondaga  lime 

83.  Lime,  brown,  hard 

84.  Lime,   gray,  hard 

85.  Sand,  gray,  hard;   little  salt  water 

86.  Lime,   gray,   hard 

87.  Lime,  sandy,  gray,  hard;  little  salt  water 

88.  Sand,  gray,  very  hard;  full  of  salt  water 

Casing  record 

12-inch  set  at       36  feet 

10-inch   set   at     193  feet 

8-inch  set  at     980  feet 

6-inch  set  at  1650  feet 


Thickness 

Depth 

Feet 

Feet 

28 

1085 

15 

1100 

10 

1110 

7 

1117 

3 

1120 

110 

1230 

35 

1265 

10 

1275 

45 

1320 

30 

1350 

30 

1380 

15 

1395 

40 

1435 

140 

1575 

20 

1595 

27 

1622 

103 

1725 

50 

1775 

30 

1805 

113 

1918 

52 

1970 

5 

1975 

15 

1990 

10 

2000 

15 

2015 

6 

2021 

42 

2063 

3 

2066 

19 

2085 

20 

2105 

8 

2113 

93 

2206 

14 

2220 

10 

2230 

5 

2235 

20 

2255 

19 

2274 

14 

2288 

STRUCTURE    AND    OIL    PROSPECTS    OF    EASTERN*    CLARK    COUNTY  5 

In  general,  the  important  changes  in  rock  sequence  which  should  be 
noted,  as  compared  with  conditions  in  the  old  fields  in  the  western  part  of  the 
county,  are  the  greater  thickness  of  both  the  Pennsylvania!!  beds  and  the 


Fig.  2.    Section    showing    stratigraphy    and    structure    from    the    Martinsville    pool 
to  a  well  near  Middletown,   Indiana.      (See  fig.   3.) 

Mississippian  lime,  and  the  generally  less  sandy  character  of  the  Kinderhook 
shales.    It  is  further  to  be  noted  that  the  interval  from  the  top  of  the  Missis- 


ILLINOIS    PETROLEUM 


R.  14  W. 


R.  13  W. 


R.  12  W 


<         O      O  O  J  s* 


R    14  W 


Fig.  3.     Structure  map  of  the  top  of  the  Devonian  limestone  in  Claris 


STRUCTURE    AM)   OIL   PROSPECTS   OF   EASTERN    CLARK    COUNTY 

R   10W. 


LEGEND 

Area  recommended   for 
testing 

Producing    area 

Shallow    dry    hole 

Shallow    dry   hole   pro- 
viding   contouring    data 


'ounty  and  adjoining  area,  showing  the  locations  of  dry  holes 


ILLINOIS    PETKOLEUJI 


sippian  lime  to  the  top  of  the  Devonian  lime  is  fairly  regular  throughout 
the  eastern  part  of  Clark  County  and  the  adjacent  portions  of  Indiana  in- 
cluded in  the  structure  map  (fig.  3).  The  parallelism  between  these  two 
contacts  does  not  exist  in  western  Clark  County,  and  has  only  recently  been 
known  to  exist  in  the  area  to  the  east.  Apparently  pre-Pennsylvanian 
erosion,  which  was  so  important  farther  west  on  the  high  part  of  the  main 
anticlinal  structure,  did  not  affect  the  Mississippian  lime  series  in  the  syncline 
to  the  east.  Therefore,  the  structure  of  some  of  the  upper  beds  in  eastern 
Clark  County  can  be  used  to  a  much  greater  extent  than  in  western  Clark 
County  for  determining  the  structure  of  the  Devonian  lime.  For  the  present, 
data  on  the  top  of  the  Mississippian  lime  in  eastern  Clark  County  can  be  used 
with  confidence  for  this  purpose ;  it  is  probable  that  further  detailed  work  in 
certain  areas  in  eastern  Clark  County  will  demonstrate  the  reliability  of  data 
on  certain  Pennsylvania!!  beds  for  determining  the  presence  of  deep  folding. 

A  somewhat  casual  examination  of  available  information  on  the  lithol- 
ogy  of  the  upper  part  of  the  Devonian  lime,  which  includes  the  producing 
zone  in  the  Martinsville  and  Siosi  pools,  shows  that  these  beds  are  gener- 
ally more  permeable  north  of  Clark  County,  and  are  commonly  tight  and 
less  permeable  in  southern  Crawford  County  and  in  Lawrence  County. 
The  wells  drilled  in  Indiana  are  believed  to  indicate  a  somewhat  similar 
change  from  the  southeast  to  the  northwest  and  north.  Although  it  is  prob- 
able that  the  variations  in  permeability  are  related  to  an  old  erosion  surface, 
the  data  thus  far  considered  do  not  provide  a  basis  for  a  definite  statement 
regarding  areas  in  which  favorable  permeability  of  the  Devonian  lime  will 
be  found,  except  that  such  favorable  conditions  are  demonstrated  by  oil  pro- 
duction at  Terre  Haute,  the  Siosi  pool  and  the  Martinsville  pool. 

STRUCTURE 

The  structure  of  Clark  County,  Illinois,  and  the  adjoining  part  of 
Indiana  is  shown  in  figure  3  by  contours  drawn  to  give  the  elevation  of  the 
top  of  the  Devonian  limestone  below  sea  level.  Since  all  of  the  elevations 
are  below  sea  level,  the  lowest  structures  in  the  area  are  indicated  by  con- 
tours having  the  largest  minus  elevations. 

The  principal  structural  features  of  the  area  are  the  Westfield  and 
Martinsville  domes,  the  big  dip  to  the  east  into  the  West  Union  syncline, 
and  the  rise  to  the  east  of  this  syncline  into  Indiana.  The  anticlinal  nose 
in  southern  Vigo  County,  Indiana,  where  the  present  development  is  taking- 
place,  and  the  anticlinal  nose  in  Clark  County,  Illinois,  near  Marshall,  are 
structural  features  which  appear  to  be  of  lesser  importance  at  the  present 
time,  but  it  should  be  observed  that  the  data  for  these  structures,  particu- 
larly the  latter,  are  very  general  and  it  is  possible  that  the  full  extent  of  local 
domino-  is  not  vet  realized. 


STRUCTURE   AND   oil     PROSPECTS   OF   EASTERN    CLARK    COUNTY  9 

The  structure  of  the  Westfield  area  has  been  taken  from  a  map  in  a 
detailed  report  now  in  press,1  and  the  structure  of  the  Martinsville  pool 
from  a  map  published  in  a  previous  number  of  Illinois  Petroleum.2  Except 
in  the  Siosi  pool  the  wells  which  provided  data  used  in  contouring  outside 
of  these  areas  are  indicated  on  the  map  by  serial  numbers  which  refer  to 
their  further  identification  in  a  table  at  the  end  of  the  report.  The  other 
wells  shown  on  the  map  are  reported  to  have  been  drilled  in  the  locations 
shown,  but  no  records  giving  data  which  could  be  used  to  determine  geologic 
conditions  are  available.  For  most  such  wells  only  the  approximate  total 
depth  is  known. 

In  preparing  the  structure  map  a  contour  interval  of  100  feet  is  used 
because  o\  the  small  scale  of  the  map,  the  size  of  the  structures  mapped,  and 
the  considerable  areas  in  which  no  data  are  available.  Outside  of  the  areas 
previously  mapped  the  well  elevations  were  determined  by  barometric 
methods,  but  the  limits  of  error  from  this  source  are  too  small  to  introduce 
any  important  modification  of  the  map.  For  most  of  the  other  maps  recently 
published  the  Illinois  Geologic  Survey  has  used  a  contour  interval  of  either 
10  or  25  feet.  In  comparison  with  such  maps  the  structures  shown  in  figure 
3  by  the  100-foot  contours  do  not  appear  as  important  as  their  relative  size 
would  indicate  unless  the  difference  in  contour  interval  is  kept  in  mind. 

The  presence  of  an  anticlinal  nose  or  terrace  near  Marshall,  Illinois,  is 
one  of  the  most  important  facts  brought  out  by  this  investigation.  Two  ol 
the  three  wells  which  provided  the  data  by  which  this  structural  feature 
was  determined  did  not  reach  the  Devonian  limestone ;  one  of  them  did  not 
even  reach  the  Mississippian  limestone,  but  correlations  which  seem  to  be 
clearly  indicated  by  a  comparison  of  the  logs  of  these  wells  show  that  there 
is  a  locally  high  structure  in  the  area  outlined  on  the  map.  Available  data 
do  not  permit  a  conclusion  as  to  the  size  or  exact  location  of  this  structure, 
but  it  is  apparent  that  it  is  of  sufficient  size  to  merit  testing  for  possible 
production  in  the  Devonian  limestone. 

RELATION  OF  OIL  ACCUMULATION  TO  GEOLOGIC  FEATURES 

A  combination  of  local  structure  and  regional  permeabilitv  within  the 
producing  zone  determines  the  occurrence  of  commercially  important  pools 
of  oil  in  the  Devonian  limestone.  On  the  Westfield  dome  and  on  the  Oak- 
land dome  to  the  north  in  Edgar  County,  Illinois,  the  limestone  was  found 
to  be  so  open  and  permeable  that  very  little  oil  remained,  even  on  the  high 
parts  of  these  big  structures.     In  the  Martinsville  pool  the  producing  zone 


1  Mylius,   L.  A.,  Oil  and  gas  in  eastern  Illinois:   Illinois  State  Geol.   Survey  Bull.   54. 
PI.  XXVI.      (In  press.) 

:  Moulton,  Gail   P.,  Areas  for  further  prospecting  near  the  Martinsville  Pool,  Clark 
County:    Illinois  State   Geol.   Survey   Illinois  Petroleum  No.   4,   August   28,   1926. 


10  ILLINOIS    PETROLEU.M 

is  almost  too  permeable  to  permit  the  accumulation  of  an  important  amount 
of  oil,  as  is  shown  both  by  the  abundance  of  water  produced  with  it,  and  the 
low  saline  content  of  the  water. 

In  other  parts  of  the  area  the  permeability  of  the  upper  part  of  the 
Devonian  lime  is  so  restricted  that  its  flow  capacity  is  very  small,  and 
although  oil  accumulates  in  it,  even  on  small  structures,  the  rate  of  produc- 
tion is  so  slow  that  the  wells  are  not  profitable.  The  Riley  pool  in  south- 
eastern Vigo  County,  Indiana,  is  an  example  of  this  type  of  condition. 

In  areas  with  an  intermediate  permeability  in  the  Devonian  producing 
zone,  wells  drilled  on  favorable  structures  will  consistently  yield  satisfactory 
production.  The  Siosi  pool  is  believed  to  be  typical  of  such  favorable  com- 
bination of  conditions. 

The  effect  of  structure  in  determining  the  producing  area  in  the  Mar- 
tinsville pool  is  very  marked  for  the  production  from  the  Devonian  lime. 
The  boundaries  of  the  producing  area  and  the  structure  contours  are  closely 
parallel.  Wells  drilled  high  on  the  structure  were  characterized  by  their 
comparative  freedom  from  water  troubles.  Successively  lower  wells  on  the 
structure  had  increasingly  larger  proportions  of  water  to  oil,  until  at  the 
edge  of  the  producing  area  the  proportion  of  oil  found  was  too  small  to 
make  pumping  profitable.  A  similar  close  relation  between  structure  and  the 
producing  area  seems  to  be  indicated  by  the  present  development  in  the  Siosi 
pool,  and  is  to  be  expected  for  any  other  pools  which  may  be  discovered  in 
the  Devonian  limestone.  The  uniformity  of  permeability  is  also  important 
to  oil  producers  because  more  uniform  rates  of  production  will  be  found 
over  such  a  field  than  is  usually  true  in  the  Illinois  region  for  wells  producing 
from  sandstones. 

These  considerations  lead  to  the  conclusion  that  oil  producers  desiring 
to  develop  production  from  the  Devonian  lime  should  first  determine  the 
location  of  large  areas  which  appear  to  have  suitable  permeability  in  the 
producing  zone  of  the  Devonian  limestone,  and  then  should  attempt  to  locate 
favorable  structures  in  such  an  area.  One  area  which  is  thought  to  meet  both 
these  requirements  is  described  in  this  report. 

Although  it  is  not  believed  that  any  rule  of  thumb  method  of  determin- 
ing the  proper  permeability  of  the  producing  zone  of  the  Devonian  lime- 
stone can  be  given  at  present,  it  seems  probable  that  mineral  analyses  of  the 
water  found  in  any  wells  drilled  to  this  bed  in  the  future  should  give  a  sub- 
stantial basis  for  comparing  the  effectiveness  of  water  circulation  through 
the  zone  at  various  points.  The  content  of  common  salt,  for  example,  in 
water  from  the  Devonian  lime  producing  zone  in  the  Martinsville  pool  is 
only  about  half  as  great  as  that  from  the  productive  Mississippian  lime 
above.     On  a  basis  of  equal  original  salt  content  for  the  waters  in  these 


STRUCTURE    AND    OIL    PROSPECTS    OK    EASTERN    CLARK    COUNTY  11 

zones,  it  appears  that  the  effectiveness  of  fluid  movements  through  the  De- 
vonian lime  has  been  very  much  greater.  Although  the  distance  of  an  area 
from  the  point  of  inflow  of  fresh  water,  as  well  as  the  rate  of  movement  of 
water,  determines  the  amount  of  dilution  of  the  original  brines  by  waters 
percolating  through  the  rocks  later,  it  nevertheless  seems  probable  that  varia- 
tions in  distance  from  the  point  of  inflow  over  eastern  Clark  County  are  so 
small  that  they  are  of  much  less  consequence  than  the  permeability  of  the 
limestone  in  controlling  the  amount  of  dilution  which  has  taken  place.  For 
the  purposes  of  this  report  dilution  of  the  salt  content  of  the  water  is  taken 
as  directly  due  to  the  effectiveness  of  the  permeability  of  the  limestone  in 
permitting  fluid  circulation. 

At  the  present  time  it  is  believed  that  only  an  exceptionally  sharp  struc- 
ture would  be  competent  to  cause  oil  accumulation  in  the  Devonian  lime- 
stone if  it  were  more  open  than  at  Martinsville.  We  may  proceed  on  this 
basis  with  the  conclusion  that  areas  in  this  district  in  which  water  from  the 
upper  zone  of  the  Devonian  limestone  contain  less  than  about  20,000  parts 
per  million  of  sodium  chloride  (common  salt),  the  amount  present  in  the 
Martinsville  pool,  are  to  be  regarded  as  unfavorable.  A  sodium  chloride 
content  in  this  general  territory  of  from  20,000  to  30,000  parts  per  million 
is  believed  to  indicate  favorable  conditions  of  permeability  ;  waters  with  a 
much  larger  salt  content  will  probably  be  found  only  where  the  permeability 
of  the  upper  part  of  the  Devonian  limestone  is  so  reduced  that  the  possi- 
bility of  producing  oil  at  a  commercial  rate  is  doubtful. 

Recommendations 

It  is  recommended  that  wells  should  be  drilled  to  the  top  of  the  Missis- 
sippian  lime  in  eastern  Clark  County  to  determine  structural  conditions  which 
might  be  favorable  for  the  accumulation  of  oil  in  the  upper  part  of  the 
Devonian  limestone.  During  such  structure-test  drilling  it  is  advisable  to 
make  an  effort  to  detect  characteristics  of  some  of  the  Pennsylvanian  forma- 
tions which  may  permit  their  use  as  key  beds,  should  they  prove  to  have  a 
structure  essentially  parallel  to  that  of  the  Mississippian  limestone. 

It  is  recommended  that  the  area  shown  as  probably  favorable  on  the 
map  accompanying  this  report  shall  be  the  first  locality  tested  by  structure 
drilling,  for  a  favorable  structure  is  already  indicated  there  and  conditions 
of  permeability  in  the  Devonian  limestone  are  believed  to  be  favorable  for 
satisfactory  production.  To  start  this  program  of  development  several 
structure  test  wells  should  be  drilled  in  T.  11  N.,  R.  1  1  W.  in  the  following 
locations  and  preferably  in  the  following  order:  first,  NE.  J/A  sec.  19; 
second.  NW.  %  sec.  IS;  and  third.  XE.  ]/A  sec.  20.  The  first  well  should 
serve  to  test  the  interpretation  of  structure  based  on  the  data  available  at 
present.     If  this  interpretation  is  verified  within  moderate  limits,  the  other 


12  ILLINOIS    PETROLEUM 

structure  tests  should  be  drilled  for  the  purpose  of  determining  the  size  and 
exact  location  of  the  favorable  structure,  as  well  as  its  highest  part.  Deep 
drilling  then  could  be  undertaken  with  considerable  confidence,  and  the  loca- 
tions should  be  chosen  for  the  purpose  of  obtaining  further  structural  in- 
formation as  well  as  oil  production,  at  least  until  several  deep  wells  had  been 
completed.  If  the  first  test  shows  that  the  interpretation  of  structure  given 
in  figure  3  is  seriously  in  error,  an  immediate  reconsideration  of  plans  is 
advisable. 

A  program  of  this  sort  is  believed  to  be  suitable  for  either  a  large  pro- 
ducing organization,  or  for  an  association  of  smaller  producers,  for  although 
the  prospects  of  getting  oil  production  appear  to  be  fairly  good,  it  is  apparent 
that  proper  testing  of  this  locality  might  require  a  larger  expenditure  than 
the  usual  Illinois  wildcat  proposition. 

The  State  Geological  Survey  will  be  glad  to  cooperate  with  any  organ- 
ization desiring  to  undertake  the  testing  of  eastern  Clark  County,  either  in 
the  favorable  area  described  in  this  report,  or  in  other  localities  which  may 
appear  favorable  as  a  result  of  subsequent  drilling.  This  cooperation  will 
consist  of  furnishing  any  available  detailed  information  from  the  files  of  the 
Survey,  determining  the  elevations  of  wells,  interpreting  the  data  from  the 
records  of  any  wells  drilled,  and  having  chemical  analyses  made  of  the 
mineral  content  of  water  from  the  Devonian  limestone  from  any  wells 
located  in  that  part  of  Illinois. 

Tables  of  wells,  numbered  for  reference  on  map 

1.  Nattkemper  and  Connelly,  NW.  Vi  sec.  11,  T.  11  N.,  R.  10  W.a 

2.  Hodson,  sec.  7,  T.  11  N.,  R.  11  W. 

3.  Wernz,  sec.  22,  T.  11  N.,  R.  11  W. 

4.  Henbest,  sec.  19,  T.  11  N.,  R.  11  W. 

5.  Johnson  or  Cork?  sec.  16,  T.  11  N.,  R.  12  W. 

6.  Claypool,  SW.  %  sec.  1,  T.  11  N.,  R.  13  W. 

7.  J.  Stout,  NW.  %  sec.  26,  T.  10  N.,  R.  10  W." 

8.  Tutt  Mayfleld,  SW.  %  sec.  4,  T.  9  N.,  R.  10  W.!' 

9.  Welch  Bros.,  sec.  11,  T.  9  N.,  R.  11  W. 

10.  Beauchamp,  sec.  4,  T.  9  N.,  R.  12  W. 

11.  Golden,  sec.  3,  T.  11  N.,  R.  12  W. 


»  Logs  of  these  wells  were  obtained  through  the  courtesy  of  the  Indiana  State 
Geological  Survey,  Dr.  W.  N.  Logan,  State  Geologist,  Bloomington,  Indiana.  The  other 
records  were  obtained   through   the  regular  work   of  the   Illinois  Geological   Survey. 


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